The present invention relates generally to sensing circuits for use in a memory device, and more particularly, to a source side sensing circuit for use in a memory device.
For low voltage operation of a memory device, for example a xe2x80x9cFlashxe2x80x9d memory device, a sensing circuit is used to sense core cell current to determine memory data values. However, typical sensing circuits may have problems providing enough usable gain, and as a result, it may difficult to accurately determine memory data values.
FIG. 1 shows a conventional sensing circuit 100 for use with a memory device. A core cell current (I0) derived from a core cell 102 is sensed by a resistor 104. The current appears as a voltage (SAIn) that is coupled to a comparator 106 and compared to a reference signal. The comparator 106 produces a core cell data value as a result of the comparison. The fixed resistor 104 is used to convert the core cell current I0 to a voltage for comparison.
FIG. 2 shows another conventional sensing circuit 200 for use with a memory device. The core cell current I0 is coupled to a drain of transistor 202. During operation, when the transistor is turned off, the SAIn node starts increasing in voltage. The SAIn voltage will be dependant on the core cell data.
Unfortunately these conventional sensing circuits may have problems providing enough gain or voltage differential on the SAIn terminal for accurate comparison. Therefore is would be desirable to have a sensing circuit that overcomes the problems associated with conventional sensing circuits.
The present invention includes a system for source side sensing in a memory device. The system includes a constant current source to determine a core cell current and a cascode circuit to convert the core cell current to an output voltage. The output voltage is used to compare to a reference signal to determine the data value of the memory cell.
In one embodiment of the invention, a source side sensing circuit for use in a memory device to determine core cell data from core cell current is provided. The source side sensing circuit includes a constant current source coupled to receive the core cell current, and a cascode circuit coupled to the constant current source to convert the core cell current to an output voltage that is representative of the core cell data.
In another embodiment of the invention, a method for source side sensing a core cell current in a memory device is provided. The method includes steps of coupling the core cell current to constant current source, coupling a cascode current provided by a cascode circuit to the constant current source, and converting the cascode current to an output voltage that is representative of the core cell current.